Lack of Correlation Between the Mean
Tender Point Score and Self-Reported Pain in
Fibromyalgia
Johannes W G. Jacobs, Johannes J. Rasker, Agnes van der Heide, Johannes W Boersma,
Alida C. E. de Blkcourt, Eduard N.Griep, Martin H. van fijswjjk, and Johannes W J. Bijlsma
Objectives. To study the validity and nature of self
assessed symptoms among patients with fibromyalgia
syndrome (FMS) and to compare our data with findings
reported in the US. To determine whether tender point
scores correlate with self-reported pain and other symptoms and to study the influence of disease duration.
Methods. Tender point scores were assessed in 113
consecutive patients with FMS. All patients completed
2 self-assessment questionnaires [an extended Campbell list, the Enschede Fibromyalgia Questionnaire, and
the Dutch Arthritis Impact Measurement Scales).
Results. The selfassessed symptoms of the Dutch
FMS patients seem to be valid and are comparable with
those of American patients. No association between
disease duration and number of self-reported symptoms was found. An association between self-reported
pain and mean tender point score was lacking for patients with disease of shorter duration and was weak
for patients with disease of longer duration.
Johannes W. G. Jacobs, MD, P M , Professor Johannes W. J. Bijlsma,
MD, PhD, Rheumatologists, Agnes van der Heide, MD, P M , Research Fellow, Department of Rheumatology, University Hospital
Utrecht; Professor Johannes J. Rasker, MD, PhD, Rheumatologist,
Hospital Medisch Spectrum Twente; Johannes W. Boersma, MD,
Rheumatologist (retired), Arnhem; Eduard N. Griep, MD, Rheumatologist, Hospital Medisch Centrum Leeuwarden; and Professor
Martin H. van Rijswijk, MD, PhD, Rheumatologist, and Alida C. E.
de Bkcourt, MD, PhD, Rehabilitation Specialist, University Hospital
Groningen, The Netherlands.
Address correspondence to Johannes W. G. Jacobs, MD, PhD, University Hospital Utrecht, Department of Rheumatology, F 02.223,
P.O. Box 85500, 3508 GA Utrecht, The Netherlands.
Submitted for publication January 19, 1995; accepted in revised
form October 6, 1995.
0 1996 by the American College of Rheumatology.
0893-7524/96/$5.00
Conclusions. The use of a self-report questionnaire
for patients with FMS is feasible and appears to be
valid. Tender point scores and self-reported pain represent very different aspects of pain in FMS.
Key words. Fibromyalgia; Self-assessment; Tender
points; Pain.
INTRODUCTION
The fibromyalgia syndrome (FMS)is a puzzling nonarticular rheumatic syndrome characterizedby chronic,
widespread musculoskeletalpain as the most prominent
symptom, and marked tenderness to pressure at specific
sites on physical examination (1-3). These so-called
tender points lie at the insertion of tendons, ligaments,
and muscles. There are no signs of joint or soft tissue
inflammation, and joint deformity does not develop. In
addition to pain, various other (nonspecific)complaints
are fiequently reported by patients with FMS,such as
sleep disturbance, fatigue, paresthesia, anxiety, headache, and morning sti&ess (1-7). Clinically, there is a
major overlap between F M S and other pain and fatigue
syndromes, e.g., chronic fatigue syndrome, irritable
bowel syndrome, and tension headache, which suggests
that FMS might not be a homogeneous entity (6).
In contrast to rheumatoid arthritis, for which firm
correlations between symptoms, e.g., pain and joint
scores on physical examination,have been found, there
is a lack of correlation between symptoms and tender
point scores in F M S (6,7). This might be due to low
reliability of the symptoms and/or tender point scores.
However, tender point scores seem to be reliable (8).
Another possibility, of course, is that tender point
105
106 Jacobs et a1
scores and symptoms are indeed independent, entirely
differentaspects of FMS. This would be very intriguing
with respect to the pathophysiology of FMS.
There is no generally accepted method for the assessment of symptoms in FMS. Since the many nonspecific symptoms of FMS may be subject to major
observer interpretation, self-assessment might be the
best approach. In some studies, e.g., the investigation
resulting in the American College of Rheumatology
(ACR) classification criteria, the self-administered
questionnaire developed by Campbell et a1 was used
(2,3).This questionnaire is considered to be very useful
both clinically and for research purposes (3), although
it has not yet been validated.
The aims of the present study were: 1)to investigate
whether self-assessmentof symptoms by patients with
FMS using a Dutch version of the Campbell questionnaire is feasible and valid, 2) to gain insight into the
prevalence and nature of symptoms in a series of patients with established FMS in The Netherlands and
to compare these data with findings reported in the
US, and 3) to study the correlation between tender
point scores and self-assessedpain as well as other selfassessed symptoms, and to investigate the influence of
disease duration.
PATIENTS AND METHODS
Patients. Consecutive outpatients with primary FMS
visiting 3 rheumatology departments in The Netherlands were asked to participate. In all cases, the diagnosis was established on the basis of the criteria of
Yunus (1). To avoid selection bias, no FMS classification criteria were set for inclusion at the start of the
study. Since the severity of signs and symptoms may
fluctuate in FMS, as in other rheumatic diseases, the
use of such inclusion criteria would not have been
compatible with our intention that the results of the
study be applicable to the population of FMS outpatients visiting Dutch rheumatology departments.
Variables. All patients completed the Enschede Fibromyalgia Questionnaire (EFQ, a Dutch extended version of the self-report Campbell questionnaire (2).The
15 items of this questionnaire were translated; 8 items
concerning irritable bowel syndrome,neurologic symptoms, and the (lack 00 effect of analgesics were added
because they are frequently reported in association with
FMS. Thus, the EFQ consists of 1 7 items about symptoms and complaints and 6 items about factors which
can modulate pain and well-being. For each question,
there were 4 responses: “never,” “sometimes,” “often,”
and “almost always” (Table 1). With regard to the re-
Vol. 9, No. 2 , April 1996
Table 1. Ranked scores for the items of the Enschede
Fibromyalgia Questionnaire
Symptoms
I have pain in my muscles and joints
I tire easily
I have pain in my neck and shoulders
I am stiff in the morning
I ache in the morning
I wake up frequently at night
I have regular bowel movementst
I am too tired during the day to do what I want to do
My hands and feet feel as if they are swollent
Pain wakes me up at night
I have “pins and needles” in my hands and feett
I have headachest
I have anesthetized sensations in my hands and feett
I have abdominal painst
I suffer from flatulencet
I sleep well at night
I feel well rested when I get up in the morning
96
93
88
85
84
73
68
68
64
62
60
56
55
31
25
23
11
Modulating factors
My pain is affected by the weather
Heat (such as a heating pad) helps my pain
I have more pain when I am emotionally upset
Exercise makes me feel better
Analgesics are effective for my paint
My pain is worsened by noise
67
41
34
30
20
16
* After transformation of ”never” and “sometimes” into “no” and “often,”
and “almost always” into “yes.”
t The 8 items of the questionnaire that were added to the 15 original items
of the Campbell questionnaire.
sponses, the period of time to be taken into consideration was not stated, as in the original version.
To assess symptoms not covered by the EFQ, such
as health perception, anxiety, and depression, and to
get a second self-assessed measure of pain, the Dutch
version of the Arthritis Impact Measurements Scales
(Dutch AIMS) was also completed; the scores were
transformed into scale scores ( 9 , l O ) .
The 14 tender points described by Smythe were assessed by the investigators (JWGJ, JWJB, ACEDB) who
used the thumb or the second finger to apply a pressure
of approximately 4 kg (4).The following scoring system
was used for grading the severity of the resulting pain:
0 = no pain; 1 = mild pain, no grimace, 2 = spontaneous verbal reactions to pain, and grimace, and 3 =
severe pain with withdrawal. We had used this scoring
system in previous studies of patients with FMS
(8,11,12).The reliability of this manual palpation method (mean test-retest and inter-observergeneralizability
coefficients [Cronbach’s a] of 0.74 and 0.71, respectively) is equal to that of the pressure algometer (8).
For each patient, the mean of the scores for the 14
tender points was calculated, and the number of tender
Arthritis Care and Research
Table
2.
Mean Tender Point Score and Pain in Fibromyalgia 107
Characteristics of the 3 patient groups
All centers
Arnhem
Enschede
Groningen
113
7
106
31
2
29
47
2
45
35
3
32
Mean age (SD)
48 (10)
45 (9)
50 (11)
47 (10)
Mean disease duration in years (SD)
Range
25-75 percentiles
1 3 (10)
10 (9)
2.0-35.0
3-15
1 5 (11)
0.5-45.0
6-1 6
0.5-45.0
7-20
12 (7)
5.0-40.0
8-15
Mean tender point score (SD)”
Range
25-75 percentiles
1.4 (0.5)
1.8 (0.5)
1.3 (0.4)
1.3 (0.4)
0.1-2.9
1.1-1.a
1.0-2.9
1.3-2.1
0.4-2.1
1.0-1.6
0.1-2.1
1.1-1.6
Mean number of tender points (SD)*
Range
25-75 percentiles
11 (2.8)
1 3 (1.7)
11 (2.7)
11 (3.3)
1-14
10-14
9-14
12-14
4-14
9-1 3
1-14
9-13
Mean number of symptoms (SD)t
Range
25-75 percentiles
11 (3)
3-1 7
9-14
32 (3)
12 (3)
7-1 7
10-14
3-1 7
10-14
10 (3)
4-1 7
7-1 2
Number of patients
Men
Women
* Assessing the 14 tender points according to Smythe. Mean tender point score maximum 3; mean number of
tender points maximum 14.
t Number of items on the Enschede Fibromyalgia Questionnaire scored “yes” (after transformation of “never”
and “sometimes” into “no” and “often,” and “almost always” into “yes”); the 6 modulating factors (see Table
31 were excluded. Maximum 17.
points with a score 21 (accordingto the ACR definition
of a tender point [31) was determined.
Methods of analysis. To analyze the prevalence of
self-assessedsymptoms,the responses on the EFQwere
transformed: “never” and “sometimes” became “no,”
and “often” and “almost always” became “yes,” as described previously (3). The prevalence of self-reported
symptoms using the EFQ among patients of the 3 Dutch
centers was compared. The internal consistency (Cronbach’s a)of the EFQ was investigated by subjecting the
urigind item scores to factor analysis (principal axis
factoring and varimax rotation). Items with factor loadings 20.40 for only 1 factor were retained. For this
analysis, all 6 items on modulating influences and 3
items that had a skewed distribution (absolute skewness 21: pain in muscles/joints, pain in necdshoulders, and feeling well-rested when getting up in the
morning) were excluded.
The prevalence of symptoms among Dutch patients
(using data from the EFQ and Dutch AIMS) was compared with that found for American patients with FMS
(1-3,6).
Spearman’s rank correlation coefficients between
self-assessed symptoms and the mean tender point
score were determined. The influence of disease duration on the correlation between the mean tender
point score and self-assessedpain was investigated: the
correlation of the number of tender points with self-
assessed pain was determined. To investigate whether
the number of symptoms per patient depended on disease duration, the mean number of symptoms was calculated for the groups of patients with a disease duration <lo years (n = 54) and 210 years (n = 59). The
mean number of symptoms and the disease duration
were also tested for a linear or nonlinear association
statistically, and visually on a 2-way plot.
For statistical analyses, the computer software packages SPSS/PC+ and Number Cruncher Statistical System were used (13).
RESULTS
Patient characteristics. The characteristicsof the patient groups from the 3 rheumatology departments are
shown in Table 2. There were no statisticallysignificant
or clinically relevant differences between the groups.
Of the 113 patients, only 7 were male. The mean age
was 48 years. The mean number of tender points was
11 (maximum possible 14), the mean number of selfreported symptoms, using the EFQ, was 11 (maximum
possible 17), and the mean tender point score was 1.4
(maximum possible 3).
The frequencies of each of the 1 7 symptoms assessed
by the EFQ among the patients from the 3 centers were
fairly similar (differences of less than 30%), except for
the means of 2 medical centers for “waking up at night”
Vol. 9, No. 2, April 1996
108 Jacobs e t a1
Table 3. Factor analysis of the scores of the 113 patients for the Enschede
Fibromyalgia Questionnaire
Factors and factor loading*
1
I sleep well at night
I wake up frequently at night
Pain wakes me up at night
I tire easily
I am too tired during the day to do what I want to do
I am stiff in the morning
I ache in the morning
I have regular bowel movements
I have abdominal pains
I suffer from flatulence
I have headaches
I have “pins and needlts” in my hands and feet
I have anesthetized sensations in my hands and feet
My hands and feet feel as if they are swollen
-
-
-0.74
0.70
0.73
-
0.85
-
0.83
-
0.60
3.78
Eigenvalue
% of variance explained
Cronbach’s a t
2
27.0
0.71
1.71
12.2
0.68
3
4
-
-
Table 4. Comparison of the prevalence of symptoms (Yo)
among Dutch patients and other groups of patients with
fibromyalgia syndrome*
Study (ref.)
Dutch Yunus Campbell
(present) (1)
(2)
Morning stiffness
Fatigue
Sleep disturbance
Paresthesia
Headache
Anxiety5
Irritable bowel
85
83
71
60
56
47
29
72
92
56
58$
44
70
34
91
100
ACR
Quimby
(3)
(6)
76
86
91
68t
78
76
-
67
55
-
54
45
50
36
79
63
56
37
* Methods of data collection in the American College of Rheumatology
(ACR) investigation were not described in detail (3). In our study (Dutch)
for morning stiffness, the Enschede Fibromyalgia Questionnaire (EFQ) item
“stiffness in the morning,” and for headache, the EFQ item “headaches,”
were used; for fatigue, sleep disturbance, paresthesia, and irritable bowel
syndrome, the mean percentages of the items making up the respective
factors (Table 1)were calculated.
t Waking up frequently.
Subjective swelling 32%, numbness 26%.
5 Anxiety in the Dutch group was defined as a score of 2 5 on the Anxiety
scale of the Dutch Arthritis Impact Measurement Scales (range 0-10,where
0 = no anxiety and 10 = maximum anxiety).
*
-
-0.69
0.74
0.60
1.29
9.2
0.62
* Only items with factor loading 20.40, loading on just 1 factor. Factor 1 = paresthesia; factor 2
turbance; factor 3 = irritable bowel syndrome; factor 4 = fatigue.
t For the relevant items.
(data not shown).Factor analysis yielded 3 factors consisting of 3 items and 1 factor consisting of 2 items
(Table 3). Factor 1,which describes neurologic symptoms, is called “paresthesia,” factor 2 “sleep disturbance,” factor 3, which describes abdominal symp-
0.72
0.79
1.22
8.7
0.62
=
sleep dis-
toms, “irritable bowel,” and factor 4 “fatigue.” The internal consistency of these factors (Cronbach a values)
ranged from 0.62-0.71. For research purposes, a value
of a 20.6 is considered acceptable for scales (14). Because the value of a increases with the number of items
in a scale, the values found in our study for scales
consisting of only 2 or 3 items are satisfactory. Three
items (stiffness in the morning, aching in the morning,
and headaches) were not included in the factors.
The prevalence and nature of symptoms assessed by
the EFQ are shown in Table 1;pain, fatigue, and stiffness were the most frequent symptoms. The prevalence
of the symptoms among Dutch FMS patients was, in
general, comparable to that found in American investigations (Table 4) (1-3), although there were notable
differences in the frequency of paresthesia,anxiety, and
irritable bowel between individual studies.
The 2 self-reportedmeasures of pain correlated with
many other self-reported symptoms (Table 5). This indicates that patients who reported severe pain also experienced other signs and symptoms as being of a severe intensity. The mean tender point score only exhibited a statistically significant correlation with the 2
self-reported measures of pain and sleep disturbance,
the coefficients being 0.22,0.20, and 0.19, respectively.
The correlation coefficient for the mean tender point
score and self-reportedpain (Dutch AIMS) was 0.03 (P
not significant) for patients with disease of less than
Arthritis Care and Research
Mean Tender Point Score and Pain in Fibromyalgia
109
Table 5. Correlations of self-assessed symptoms with mean tender point scores for patients with fibromyalgia syndrome*
1. Pain on the Dutch AIMSt
2. Pain on the EFQS
2
3
4
5
6
7
8
9
10
0.50
0.58
0.35
0.31
0.23
0.37
0.24
0.42
-
0.35
0.39
0.34
0.40
-
0.33
0.53
0.35
0.32
0.21
0.41
0.20
-
3. Arthritis impactt
4. Health perceptiont
5. Anxietyt
6. Depressiont
7. Fatigues
0.39
0.39
0.43
0.72
8. Paresthesias
9. Sleep disturbances
10. Irritable bowels
0.21
0.25
0.42
-
-
0.22
0.26
0.34
0.24
0.36
Mean
tender
point
score
0.22
0.20
0.27
0.22
0.22
-
0.24
0.19
-
* Horizontal item numbers correspond to vertical item numbers. Mean tender point score represents 14 tender points. Spearman’s p coefficients: all values
statistically significant: 0.19-0.24, Pbetween 0.05 and 0.01; 0.25-0.26, Pbetween 0.01 and 0.005: 0.27-0.32, Pbetween 0.005 and 0.001; and >0.32, P <0.001.
t AIMS = Arthritis Impact Measurement Scales, data from scales of Dutch AIMS.
The item “pain in muscles/joints” of the Enschede Fibromyalgia Questionnaire (EFQ).
5 Scales of the EFQ, resulting from factor analysis.
*
10 years’ duration and 0.44 (P = 0.0006) for patients
with disease lasting 210 years (Figure 1).Therefore,
19% of the variance of the mean tender point score is
explained by self-reported pain in the group with disease of 210 years’ duration, whereas self-reported pain
does not explain any of the variance in the mean tender
point score for patients with disease of <lo years’ duration. Ten years was chosen as the cut-off point because it was the median disease duration in the study.
Other cut-off points (3,4, and 5 years) were also tested.
In these analyses, the correlation between the mean
tender point score and self-reported pain remained
roughly the same, e.g., R, = 0.24, 0.26, and 0.28, respectively, for a disease duration of 23, 4, and 5 years
( P = O.OI,O.OI,and 0.009) and R, = -0.03, -0.06,and
-0.02 for disease duration of <3, 4, and 5 years ( P =
0.92, 0.81, and 0.91). The correlation coefficient for the
number of tender points with self-assessedpain (Dutch
AIMS) was 0.27 (P < 0.01).
For patients with a disease duration <10 years (n =
54), the mean number of symptoms was 11,the same as
for patients with a disease duration of 210 years (n =
59). No linear or nonlinear association between disease
duration and number of symptoms could be detected
statistically or visually on the 2-way plot (not shown).
DISCUSSION
The prevalence and nature of self-reported symptoms
among patients of 3 Dutch centers were comparableand,
in general, were similar to those found for American
patients (1-3). This demonstrates that patients are able
to complete the EFQ self-report questionnaire and that
the results are consistent (14). This, together with the
results of factor analysis, indicates that the self-reported
items are valid; however, many more aspects of validity
of the EFQ are yet to be investigated.
The prevalence of Dutch self-reported symptoms corresponds best to the prevalence of symptoms reported
in the ACR study (Table 4). In both studies, FMS classification criteria were not set for inclusion;the samples
of patients were clinical ones. Also in both studies, the
Campbell questionnaire was applied. This implies that
both the study population and the method of assessment
are probable causes of differences in the prevalence of
symptoms between the reported studies in Table 4. This
underscores the need for a generally accepted instrument to assess the symptoms in FMS, and our findings
do not necessarily apply to a research sample in which
the ACR classification criteria are used for inclusion.
In our study, there was a lack of correlation between
self-assessed symptoms and the mean tender point
score (Table 5). This is in agreement with the study by
Quimby et a1 (6),who found that none of the symptoms
of Yunus’ minor criteria of FMS correlated with the
number of tender points for patients with generalized
nonarticular rheumatism. The lack of correlation between the 2 self-reported measures of pain and mean
tender point score in our study is particularly remarkable. It does not seem likely that this is attributed to
our having assessed the 14 tender points according to
Smythe instead of the 18 tender points of the ACR
criteria, because most of these tender points are the
same, or to the fact that 14 tender points were used
whereas there are so many more potential tender points
in the human body. This lack of correlation between
self-reported pain and mean tender point score is con-
Vol. 9, No. 2, April 1996
110 Jacobs et a1
A. Patients with disease duration of
< 10 years (n=54, r,
=
0.03,p=0.82):
0
aeo
0
B: Patients with disease duration of 2
101
0
10 years (n=59, r, = 0.44,p= O.ooo6):
0 0
00
0 0
0 0
0
0
0
0
01
0
1
2
3
Figure 1. Self-reported pain [y-axis) plotted against mean
tender point score (x-axis). Mean tender point score = the
mean of 14 tender points, ranging from 0 [no pain) to 3
(maximum pain). Pain = the self-report scale “Pain” of the
Dutch Arthritis Impact Measurement Scales, ranging from
0 (no pain) to 10 (maximum pain). Each dot on the plots
represents one patient; the lines are the least square regression lines. For all 113 patients, R,between self-reported pain
scores and mean tender point score was 0.22.
sistent with the observation that physical exercise resulted in increased pain, whereas the number of tender
points hardly increased (15). Burckhardt et a1 also
found no correlation between self-reported pain, as assessed by the Fibrositis Impact Questionnaire, and the
number of tender points in 2 5 FMS patients (7). Wolfe
et a1 reported that in a sample fiom the general population, self-reported pain was also not associated with
tender point counts (16). In another investigation involving the general population, it was found that
tender point counts were associated with measures of
depression, fatigue, and poor sleep, independent of the
pain status (17). It may be concluded that tender point
scores and self-reported pain represent very different
aspects of pain.
This is intriguing with respect to the pathophysiology of FMS and the origin of pain in this syndrome.
Although injections of a local anesthetic into tender
points have been shown to provide relief of local pain
(18),supporting the theory that it may result from repetitive strain or metabolic disorders of the muscles
(19,20), studies of muscles and tender point sites by
means of biopsies and other techniques have not revealed specific abnormalities (19-24). It seems more
likely that signal misinterpretation, neuroendocrine
disorders, secondary hyperalgesia,and aberrant central
pain mechanisms and pain memory are the keys to the
etiology of FMS (1525-31). This may explain why tricyclic antidepressants-in contrast to nonsteroidal
antiinflammatory drugs-may provide (moderate) relief of pain (18,19,31,32),why electroacupuncture is
effective, and why conflicting results are reported for
the effect of muscle relaxants ( 3 3 3 ) . It must be noted,
however, that at this time, these “centrally oriented”
hypotheses are mainly speculative and that there are
findings which are not compatible with these theories,
e.g., the altered interleukin secretion in FMS (35). Further research into the effectiveness of different therapeutic strategies might improve our understanding of
the pathogenetic mechanisms of FMS.
It is remarkable that in our series, patients with FMS
of shorter duration did not exhibit a correlation between self-reported pain and the mean tender point
score, in contrast to patients with disease of longer
duration. The a priori hypothesis that in FMS of shorter
duration, there might possibly be a correlation between
self-reported pain and tender point score that is lost
with progression of the disease as pain behavior further
develops does not hold. The finding cannot be easily
explained. However, to investigate the relationship between signs and symptoms and disease duration more
properly, prospective, longitudinal, long-term investigations are needed.
The self-reported symptoms of patients with FMS
can be used in experimental and clinical situations.
The prevalence of the symptoms were comparable to
those reported in the literature. The expectation that
FMS patients with a high mean tender point score
would also have a high pain score and vice versa was
not confirmed. It is recommended that for pain measurement in patients with FMS in experimental and
clinical situations,both tender points and self-reported
pain should be assessed, since they represent quite different aspects of pain.
We thank Professor F. W. Kraaimaat, PhD, and R. Geenen, PhD,
Psychologists (Department of Psychology, University Hospital
Utrecht), and E. Taal, PhD, Psychologist (Department of Psychology,
University Twente, Enschede) for their advice.
Arthritis Care and Research
Mean Tender Point Score and Pain in Fibromyalgia
REFERENCES
1. Yunus M, Masi AT, Calabro JJ, Miller KA, Feigenbaum
SL: Primary fibromyalgia (fibrositis): clinical study of
50 patients with matched normal controls. Semin Arthritis Rheum 11:151-171, 1981
2. Campbell SM, Clark S, Tindall EA, Forehand ME, Bennett RM: Clinical characteristics of fibrositis. I. A “blinded,” controlled study of symptoms and tender points.
Arthritis Rheum 26:817-824, 1983
3. Wolfe F, Smythe HA, Yunus MB, Bennett RM, et al: The
American College of Rheumatology 1990 criteria for the
classification of fibromyalgia: report of the Multicenter
Criteria Committee. Arthritis Rheum 33:160-172, 1990
4. Smythe H: “Fibrositis” and other diffuse musculoskeletal syndromes. In, Textbook of Rheumatology. Second
edition. Edited by WN Kelley, ED Harris Jr, S Ruddy,
CB Sledge. Philadelphia, WB Saunders, 1985
5. Simms RW, Goldenberg DL: Symptoms mimicking neurologic disorders in fibromyalgia syndrome. J Rheumatol 15:1271-1273, 1988
6. Quimby LG, Block SR, GratwickGM Fibromyalgia: generalized pain intolerance and manifold symptom reporting. J Rheumatol 15:1264-1270, 1988
7. Burckhardt CS, Clark SR, Bennet RM: The Fibromyalgia
Impact Questionnaire: development and validation. J
Rheumatol 18:728-733, 1991
8. Jacobs JWG, Geenen R, van der Heide A, Rasker JJ, Bijlsma JWJ: Are tender point scores by manual palpation
reliable? An investigation into the variance of tender
point scores. Scand J Rheumatol 245243447, 1995
9. Taal E, Jacobs JW,
Seydel ER, Wiegman 0, Rasker JJ:
Evaluation of the Dutch Arthritis Impact Measurement
Scales (Dutch-AIMS] in patients with rheumatoid arthritis. Br J Rheumatol 28:487491, 1989
10. Jacobs JWG, Oosterveld FGJ, Deuxbouts N, et al: Rheumatoid arthritis patients’ opinions about their own functional capacity: how valid is it? Ann Rheum Dis 51:
765-768, 1992
11. Jacobs JWG, Rasker JJ, van Riel PLCM, Gribnau FWJ,
van de Putte LBA: Behandeling met Rheumajecta en
Vasolastine van primaire fibromyalgie: resultaten van
een gerandomiseerd, placebo-gecontroleerd, dubbelblind onderzoek. Ned Tijdschr Geneeskd 134:693697, 1990
12. Rasker JJ, Jacobs JWG: Fibromyalgia, difficulties in assessing effect of therapy. Clin Exp Rheumatol5 (suppl):
P311, 1987
13. NoruSis, MJ: SPSS/PC+ V2.0 Base Manual. Chicago,
SPSS Inc., 1988
14. Nunnally JC: Psychometric Theory. Second Edition.
New York, McGraw Hill, 1978
15. Van Denderen JC, Boersma JW,Zeinstra P, Hollander
AP, van Neerbos BR Physiological effects of exhaustive
physical exercise in primary fibromyalgia syndrome
(PFS): is PFS a disorder of neuroendocrine reactivity?
Scand J Rheumatol 21:35-37, 1992
16. Wolfe F, Ross K, Anderson J: Tenderness, pain thresh-
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
111
old, and their correlates in the general population (abstract). Arthritis Rheum 36 (suppl 9):S220, 1993
Croft P, Schollum J, Silman A: Population study of
tender point counts and pain as evidence of fibromyalgia. BMJ 309:696-699, 1994
Masi AT, Yunus MB: Fibromyalgia-which is the best
treatment? A personalized, comprehensive, ambulatory,
patient-involved management programme. Baillieres
Clin Rheumatol 4:333-370, 1990
Bennett RM: Beyond fibromyalgia: ideas on etiology and
treatment. J Rheumatol Suppl 19:185-191, 1989
Bengtsson A, Henriksson KG, Larsson J: Reduced highenergy phosphate levels in the painful muscles of patients with primary fibromyalgia. Arthritis Rheum 29:
817-821, 1986
Von Miehlke K, Schulze G, Eger W: Klinische und experimentelle untersuchungen zum fibrositissyndroom.
Z Rheumaforsch 19:310-333, 1960
Bartels EM, Danneskiold-Sams~reB: Histological abnormalities in muscle from patients with certain types of
fibrositis. Lancet i:755-757, 1986
Car0 XJ: Immunofluorescent studies of skin in primary
fibrositis syndrome. Am J Med 81 (suppl 3A]:4349, 1986
Yunus MB, Kalyan-Raman UP, Kalyan-Raman K, Masi
AT Pathologic changes in muscle in primary fibromyalgia syndrome. Am J Med 81 (suppl 3A):3842, 1986
Harvey AR: Neurophysiology of rheumatic pain. J Orthop Rheumatol 3:187-194, 1990
Harvey AR A neurogenic model for soft-tissue rheumatism and its implications for management. J Orthop
Rheumatol 3:231-242, 1990
Yunus MB: Towards a model of pathophysiology of fibromyalgia: aberrant central pain mechanisms with peripheral modulation. J Rheumatol 19:846-850, 1992
Neeck G, Riedel W: Thyroid function in patients with fibromyalgia syndrome. J Rheumatol 19:1120-1122, 1992
Griep EN, Boersma JW,de Kloet ER: Altered reactivity of
the hypothalamic-pituitary-adrenalaxis in the primary fibromyalgia syndrome. J Rheumatol 20:469474, 1993
Cohen ML, Quintner JL: Fibromyalgia syndrome, a
problem of tautology. Lancet 342:906-909, 1993
Jacobs JWG, Rasker JJ, Griep EN: Fibromyalgia: a stress
related, neuroendocrine disorder? A hypothetical
framework on the aetiology and perseverance of the syndrome. Rheumatol Eur 24 (suppl 2):274-276, 1995
Bennett Rh4, Gatter RA, Campbell SM, Andrews RP, Clark
SR, Scarola JA: A comparison of cyclobenzaprine and placebo in the management of fibrositis: a double-blind controlled study. Arthritis Rheum 31:1535-1542, 1988
Pattrick M, Swannell A, Doherty M: Chlormezanone in
primary fibromyalgia syndrome: a double blind placebo
controlled study. Br J Rheumatol 32:55-58, 1993
Deluze C, Bosia L, Zirbs A, Chantraine A, Vischer TL:
Electroacupuncture in fibromyalgia: results of a controlled trial. BMJ 305:1249-1252, 1992
Hader N, Rimon D, Kinarty A, Lahat N: Altered interleukin-2 secretion in patients with primary fibromyalgia
syndrome. Arthritis Rheum 34:866-872, 1991